The invention relates to a device for delivering single-phase or multiphase fluids without altering the properties thereof.
Especially less stable multiphase fluids, for example emulsions and dispersions, which can experience irreversible changes by an energy insertion, can disadvantageously get during the delivery in corresponding devices, like pumps, into instable areas.
A very sensitive fluid system is blood. This opaque red body liquid of vertebrate animals circulates in a closed vascular system, wherein the rhythmical contraction of the heart presses the blood into the different areas of the organism. In this case the blood transports the respiratory gases, which are oxygen and carbon dioxide, as well as nutrients, metabolic products and body own substances. In this case, the blood vascular system including the heart is hermetically sealed from the environment, so that the blood experiences no changes in the healthy organism, when it is pumped via the heart through the body.
It is known, that the blood tends, when contacting with materials foreign to the body or through foreign energy affect, to a haemolysis and a thrombi formation. The formation of thrombi can be deadly for the organism, as they lead to a clogging up in the far branched vascular system. Haemolysis describes the condition, that the red blood cells are lysed destroyed further than the physiological degree. The causes for the haemolysis could be mechanical or metabolical. Increased haemolysis causes multiple organ damage and can lead to the death of the human being.
On the other hand it has been shown, that it is principally possible to support the pump capacity of the heart under specific constructive conditions or even to replace the natural heart by an artificial heart, but a constant operation of implanted heart support pumps or artificial hearts is at the moment only limitedly possible, as the interaction of these artificial products with the blood still lead to disadvantageous changes of the blood.
In the known State of the Art different development directions of blood pumps are distinguishable. Heart support pumps and artificial hearts can be designed starting from the required pressure difference and the volume flow, as well as the displacement principal as a so-called pulsating pump or according to the turbo principle as a radial or axial flow device. At the moment these three named designs are developed in parallel. The flow devices show because of the high capacity density of this type of devices smaller dimensions than piston devices. Within the group of pumps, which function according to the turbo principal, the axial pump variant is as a rule smaller than the radial variant. A turbo device can be designed generally for the given pressure difference and the given volume flow very differently, for example as an axial or a radial pump with greatly different rotational speeds.
The axial blood pumps known from the State of the Art, comprise generally an outer cylindrical pipe, in which a delivery element rotates, which is formed as a rotor of a motor stator arranged outside and which, therefore, transports the blood in an axial direction. The support of the delivery element is a problem. A purely mechanical support is disadvantageous because of the damage of the blood and even because of the relatively high friction values. Also the up-to-now described magnet bearing types have not lead to a satisfactory solution.
From Kawahito et al.: In Phase 1 Ex Vivo Studies of the Baylor/NASA Axial Flow Ventricular Assist Device, in: Heart Replacement Artificial Heart 5, pages 245-252, Springer Verlag Tokyo 1996, Publisher T. Akutso and H. Koyagani, an axial blood pump according to the state of the art for the support of an ill heart is known, which can be implanted into the chest area of a patient. The axial blood pump has a rotating impeller with a blading, which is supported within a blood carrying pipe and is driven by means of an electric motor.
For this the impeller is formed as a rotor of the electric motor and is coupled by means of magnets mounted on the blading with the stator of the electric motor fast with the housing. An axial and a radial support of the rotor takes place via a toe bearing , in which the rotor is supported point-by-point on bearing elements arranged in the flow. Such an arrangement is also known from U.S. Pat. No. 4,957,504.
The known blood pump has the disadvantage, that the to be delivered blood experiences in a considerable extent a traumatisation and damage. In this case the danger lies generally in the formation of thrombi. The reason for this lies essentially in the formation of wake areas of the bearings.
A further disadvantage is undoubtedly the limited endurance of the mechanical bearing because of wear.
U.S. Pat. No. 4,779,614 discloses an implantable axial blood pump, which consists of an outer cylindrical pipe and a rotor hub rotating in this pipe for the blood delivery. The rotor is magnetically supported and carries at the same time the rotor magnets of the drive and the impeller blades. The magnetically supported rotor forms with the stator blading mounted on the outer pipe long, narrow gaps. The arrangement of two motor-stator-combinations respectively on the ends of the pump shall stabilize the positioning of the rotor. The positioning in the direction of the axis is stabilized by another pair of magnets, which shall take up the axial forces of the rotor as well. Although a relatively wide annular gap for the fluid flow is provided and with the magnetic bearing of the rotor important development goals for the implantable blood pump concerning a compact design and free from sealing and support problems can be aimed at, the blood pump has great disadvantages concerning the function and the structural design of the pump. The exceptionally long narrow gaps between the rotor hub and the stator blades on the stator increase the danger of a blood damage by high velocity gradient of the gap flows. The arrangement of two motors required for the rotor stabilization is designwise cumbersome. Furthermore, the rotor is not form-fittingly secured in the axial direction and is therefore a residual risk.
The U.S. Pat. No. 5,385,581 also discloses an axial blood pump with magnet bearing. The bearing magnets arranged in the rotor and in the stator area are charged with an opposing polarity.
Disadvantageously this leads to the breakdown of the pump, when the bearing fails. Furthermore, it is disadvantageous that no so-called post guide lattice is provided, i.e. the total pressure is produced by the impeller, and the residual spin energy remains in the flow.
A further axial blood pump with magnetic bearing is known from WO97/49 440. The magnetic bearing is carried out at the conically formed rotor ends of the rotor, which forms the impeller. The fixedly arranged pole shoes are arranged opposite to the rotor ends, which pole shoes guide the flow of the permanent magnets. The bearing necessitates an active stabilization with at least four stabilization coils in axial as well as in radial direction. In a further variant the bearings with radially magnetized permanent magnet rings with changing magnetization direction are proposed, which are indeed difficult to control.
From WO 98/11 650 a further axial blood pump with a so-called bearingless motor is known. The xe2x80x9cbearinglessxe2x80x9d motor is a combination of a motor and a magnetic bearing. The position of the rotor is stabilized passively by permanent magnets with reference to three degrees of freedom translation in the x-direction, tipping in the x- and y-direction. The passive stabilization is achieved by a permanent magnetic rotor ring, which is surrounded on the stator side by a soft iron ring. Control and driving coils, which are connected to the soft iron ring, allow a drive with reference to three degrees of freedom. The low bearing stiffness requires additional measures. Furthermore, a bearing stabilization is necessary in the x- and y-direction, which leads to a great extent of measuring technology to be applied and can result in a high heating of the pump because of the active coils.
For the delivery of chemical fluids an axial propeller pump is known from EP-A 0 856 666. The delivery element is magnetically supported between two mounting elements, which are attached in a tubular hollow body with the retention of an annular gap. The delivery element forms the rotor of a motor, which stator is arranged externally of the tubular hollow body. The magnetic bearing is achieved in the radial direction by radial magnetized permanent magnets and in the axial direction by means of electromagnetic coils, which as far as possible are decoupled from these. Radially magnetized permanent magnets necessitate a defined minimum size and small air gaps.
Therefore, the delivery gap can only be very small, which in the here present delivery task (propeller pumps produce a high pressure at a small delivery volume) which is not a hindrance for other pumps, but, however, is especially not acceptable for blood pumps.
Furthermore, the complete axial rigidity, which is very high compared to the radial rigidity because of the delivery pressure of the to be delivery medium, has to be exerted by the stabilization coils, which requires a specific current value, which leads to a corresponding energy demand and to heating. The control of the axial position slows down with increasing current value, so that the pump is only suitable for pulsating delivery tasks to a limited extent.
It is the object of the invention to provide a device for the gentle delivery of single or multiphase fluids of a simple structural design, which does not or only inconsiderably change the to be delivered fluid in its characteristics, in which wake areas and vortexing of the to be delivered fluid are minimized and a pulsating delivery is enabled.
The object is solved according to the characterizing features of claim 1.
Preferred and advantageous embodiments of the invention are given in the sub-claims.
According to this the delivery element is supported free of contact between the mounting elements, respectively separated to each by a hub gap, by means of permanent magnetic bearing elements, which are arranged in the mounting elements as well as in the delivery element, which functionally work together and which magnetic acting faces are opposed to each other and are magnetized in the axial direction and poled oppositely. Sensors for the positional detection and stabilizers for the positional correction are arranged in the mounting elements and on or in the wall of the hollow body.
The device according to the invention achieves a simple design. The permanent magnetic bearing elements necessary for the magnetic bearing, are additionally arranged to the permanent magnetic elements of the motor rotor directly on the delivery element. The magnetic bearing takes up advantageously the axial as well as the radial forces. The axial stabilization offers an active control of the axial position of the delivery element, wherein annular coils, arranged on the front face of the delivery element, produce an axial magnetic flow, which superimposes the axial magnetic flow of the permanent magnetic bearing elements and serves for the control of the axial position.
The rotor gap, which has to be provided between the external face of the delivery element and the inner face of the tubular hollow body, has to be designed in such a way, mat the motor losses as well as the flow losses generated by the gap are minimized Hereby it is important, that the generated motor losses are increasing the flier away the motor rotor is arranged from the motor stator. A smaller rotor gap on the side of the motor is to be seen as advantageous. On the other hand a smaller rotor gap leads, however, to larger friction losses of the flow and therefore, is technologically disadvantageous concerning the flow. A suitable compromise for blood pumps lies for example in the named rotor gap width of 0.5 to 2.5 mm.
An advantageous embodiment of the invention consists in that further sensors for the determination of the instantaneous blood volume flow and for the instantaneous pressure difference generated by the pump are integrated in the hubs of the axial blood pump and/or in the walls of the tubular hollow body. Both measuring values are present in the controller of the delivery device for the variance comparison and therewith opens the possibility for a control of the delivery process in the sense of a physiological optimal pulsating delivery, adapted to the natural heart action by means of a time dependent rotational speed change of the rotor or of a pulsating pump optimized in the sense of a lower energy consumption and also realised by a time dependent rotational speed change.
In a preferred way the mounting elements are formed as fluid guide units with fluid blades. Because of this flow losses are minimized.
In a further advantageous embodiment of the invention means are provided on the front face of the rotor hub, which deliver radially the fluid present in the hub gap between the fluid guide unit and the delivery element to the outside, for example radial blades, grooves, bulgings or convex formations.
A further advantageous embodiment of the invention consists in that an axially extending bore is provided in at least one of the fluid guide units, through which the to be delivered fluid passes, and which serves, that fluid present in the hub gap between the fluid guide unit and the delivery element is transported radially to the outside.
Both prementioned embodiments influence the radial pressure distribution and produce compensation flows for the prevention of dead water areas in the hub gap between the front faces of the fluid guide unit and the delivery element.
In a further embodiment of the invention the delivery element, especially the rotor hub, has two blades distanced in the axial direction. Herewith a so-called tandem grid is formed. The pressure increase to be produced by each blading row is advantageously reduced. Furthermore, this special arrangement of the rotor of the delivery device limits additionally the disturbing tipping movement of the same.